Cisco CCNA Certification Examination Tutorial: The OSPF RID

OSPF is a significant topic on your CCNA test, as well it should be. OSPF is a greatly-utilized WAN protocol, and you want to study the fundamentals prior to moving on to more intricate configurations. One particular such element is the OSPF Router ID, or RID.

The RID is the dotted decimal price by which other OSPF routers will detect a specified OSPF router. There are some appealing defaults for this price, and a command you should know to hardcode the RID. You experienced also much better know what has to come about for this command to consider effect, so let’s choose a far more in depth look at the OSPF RID.

In this case in point, R1 has an adjacency with R2 and R3 about the 172.12.123./24 frame community. R1 is the hub, with R2 and R3 as the spokes. No other interfaces are OSPF-enabled on any of the routers. Functioning demonstrate ip ospf neighbor on R1, we see some uncommon values beneath “Neighbor ID”, which is a further identify for the OSPF RID.

R1#display ip ospf neighbor

Neighbor ID Pri Condition Useless Time Tackle Interface

3.3.3.3 Complete/DROTHER 00:01:57 172.12.123.3 Serial0

2.2.2.2 Whole/DROTHER 00:01:57 172.12.123.2 Serial0

Recognize the Neighbor ID of each remote address is the loopback handle. How can that be if they’re not OSPF-enabled?

When analyzing the Router ID (RID) of an OSPF-enabled router, OSPF will normally use the numerically best IP deal with on the router’s loopback interfaces, irrespective of whether that loopback is OSPF-enabled.

What if there is no loopback? OSPF will then use the numerically maximum IP handle of the actual physical interfaces, irrespective of whether or not that interface is OSPF-enabled.

Base LINE: An interface does not have to be managing OSPF to have its IP handle utilised as the OSPF RID.

The OSPF RID can be improved, but it requires a restart or to reinitialize the OSPF routing course of action. Use the router-id command to adjust the default RID of every single router as shown, and very clear the OSPF process to do so.

R1#conf t

Enter configuration instructions, just one per line. End with CNTL/Z.

R1(config)#router ospf 1

R1(config-router)#router-id 11.11.11.11

Reload or use “crystal clear ip ospf process” command, for this to choose impact

R1#clear ip ospf method

Reset ALL OSPF procedures? [no]: of course

1d05h: %OSPF-5-ADJCHG: Approach 1, Nbr 3.3.3.3 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached

1d05h: %OSPF-5-ADJCHG: Method 1, Nbr 2.2.2.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached

Immediately after coming into the router-id command, the router console knowledgeable you that you have to reload the router or reset the OSPF procedures for this to just take effect. You enter the very clear ip ospf process command to do this. Discover that when you happen to be asked if you actually want to do this, the prompt is “no”? That is since all the OSPF adjacencies on this router will be lost and will have to start the procedure once more. That’s Alright on a observe rack, not fantastic in a generation network. Really don’t use that just one at work.

The OSPF RID is not a complicated principle, but the truth that an interface doesn’t have to be OSPF-enabled in order to have its IP handle act as the RID usually takes some obtaining used to. And bear in mind – when the router or change asks you a concern and the prompted remedy is “no”, just take a person phase back again and make guaranteed you really want to do what you happen to be about to do!